Centrifugal fan

ABSTRACT

A centrifugal fan includes an impeller, a motor rotating the impeller about a center axis, and a housing accommodating the impeller. The housing includes an intake port arranged above the impeller, an exhaust port arranged radially outward of the impeller, an annular upper flow path, and a lower flow path arranged below the upper flow path and connected to the upper flow path. The annular upper flow path can be partially arranged between a housing inner circumferential surface and the impeller in a radial direction. The upper flow path and the lower flow path are arranged to define a flow path having a scroll shape. The lower flow path extends along the housing inner circumferential surface. The lower flow path has a lower flow path terminal end opened toward the exhaust port. The lower flow path has a lower flow path start end closed with respect to the exhaust port.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a centrifugal fan.

2. Description of the Related Art

There is available a centrifugal fan which includes an air flow pathpositioned radially outward of an impeller and a wind tunnel positionedbelow the air flow path. The air discharged radially outward from theimpeller flows from the air flow path toward the wind tunnel. Then, theair is discharged to the outside from an exhaust port.

In the centrifugal fan mentioned above, the wind tunnel positioned belowthe air flow path has an annular shape. For that reason, there may be acase where a part of the air guided to the vicinity of the exhaust portthrough the wind tunnel flows toward the upstream side of the windtunnel without being discharged from the exhaust port. This poses aproblem in that a loss of airflow is generated and the efficiency of thecentrifugal fan is reduced.

SUMMARY OF THE INVENTION

In one aspect of the present disclosure, there is provided a centrifugalfan includes: an impeller arranged to rotate about a center axisextending in an up-down direction; a motor arranged below the impellerand arranged to rotate the impeller about the center axis; and a housingarranged to accommodate the impeller. The housing includes an intakeport arranged above the impeller, an exhaust port arranged radiallyoutward of the impeller, an annular upper flow path, and a lower flowpath arranged below the upper flow path and connected to the upper flowpath. The annular upper flow path is at least partially arranged betweena housing inner circumferential surface as an inner circumferentialsurface of the housing and the impeller in a radial direction. The upperflow path and the lower flow path are arranged to define a flow pathhaving a scroll shape. The lower flow path extends along the housinginner circumferential surface. The lower flow path has a lower flow pathterminal end as one circumferential end thereof opened toward theexhaust port. The lower flow path has a lower flow path start end as theother circumferential end thereof closed with respect to the exhaustport.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the preferred embodiments made withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a centrifugal fan according toone preferred embodiment.

FIG. 2 is an exploded perspective view illustrating the centrifugal fanaccording to one preferred embodiment.

FIG. 3 is a sectional view taken along line III-III in FIG. 1,illustrating the centrifugal fan according to one preferred embodiment.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3,illustrating the centrifugal fan according to one preferred embodiment.

FIG. 5 is a side view illustrating the centrifugal fan according to onepreferred embodiment.

FIG. 6 is a side view illustrating a centrifugal fan according toanother example of one preferred embodiment.

FIG. 7 is a sectional view illustrating a portion of a centrifugal fanaccording to a further example of one preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A centrifugal fan according to one preferred embodiment of the presentdisclosure will now be described with reference to the drawings. Thescope of the present disclosure is not limited to the preferredembodiment described below but may be arbitrarily changed withoutdeparting from the scope of the technical idea of the presentdisclosure. In the drawings referred to below, for the sake of makingindividual configurations easily understandable, individual structuresare sometimes shown in the reduced scale and number differing from thoseof actual structures.

In the drawings, an XYZ coordinate system is appropriately shown as athree-dimensional rectangular coordinate system. In the XYZ coordinatesystem, the Z-axis direction is a direction parallel to the axialdirection of a center axis J illustrated in FIG. 1. The X-axis directionis a direction orthogonal to the Z-axis direction and orthogonal to anexhaust port 62 illustrated in FIG. 1. The Y-axis direction is adirection orthogonal to both the X-axis direction and the Z-axisdirection.

In the following description, the extension direction of the center axisJ (the Z-axis direction is an up-down direction. The positive side (+Zside) in the Z-axis direction will be referred to as an “upper side”.The negative side (−Z side) in the Z-axis direction will be referred toas a “lower side”. The terms “up-down direction”, “upper side” and“lower side” are used merely for the purpose of descriptions and are notintended to limit the actual positional relationships or the actualdirections. Unless specifically mentioned otherwise, the direction (theZ-axis direction) parallel to the center axis J will be merely referredto as an “axial direction”. The radius direction extending from thecenter axis J will be merely referred to as a “radial direction”. Thecircumference direction about the center axis J (θ_(Z) direction),namely the direction extending around the center axis J, will be merelyreferred to as a “circumferential direction”.

In the subject specification, the phrase “extending in the axialdirection” includes not only a case where something extends strictly inthe axial direction but also a case where something extends in adirection inclined at an angle of less than 45 degrees with respect tothe axial direction. In the subject specification, the phrase “extendingin the radial direction” includes not only a case where somethingextends strictly in the radial direction, namely in the directionperpendicular to the axial direction but also a case where somethingextends in a direction inclined at an angle of less than 45 degrees withrespect to the radial direction.

FIG. 1 is a perspective view of a centrifugal fan according to onepreferred embodiment. FIG. 2 is an exploded perspective view of thecentrifugal fan according to one preferred embodiment. FIG. 3 is asectional view of the centrifugal fan according to one preferredembodiment, which is taken along line III-III in FIG. 1. FIG. 4 is asectional view of the centrifugal fan according to one preferredembodiment, which is taken along line IV-IV in FIG. 3. FIG. 5 is a sideview of the centrifugal fan according to one preferred embodiment. FIG.3 is a sectional view of the centrifugal fan according to one preferredembodiment, which is viewed in the direction orthogonal to the exhaustport 62 (in the X-axis direction). FIG. 4 is a sectional view of thecentrifugal fan according to one preferred embodiment, which is viewedfrom the upper side toward the lower side. In the subject specification,the term “side view” refers to a view seen in the X-axis direction.

As illustrated in FIGS. 1 to 3, the centrifugal fan 10 preferablyincludes a housing 20, an impeller 30 and a motor 40. As illustrated inFIG. 3, the motor 40 is accommodated within the housing 20. The motor 40is disposed radially inward of a motor cover portion 27 which will bedescribed later. The motor 40 preferably includes a shaft 41 which isconcentric with the center axis J extending in the up-down direction.The upper end portion of the shaft 41 protrudes toward the upper side ofthe motor cover portion 27 through an output shaft hole 27 a which willbe described later.

The motor 40 is disposed below the impeller 30. The motor 40 rotates theimpeller 30 about the center axis J. In the present preferredembodiment, the motor 40 rotates the impeller 30 counterclockwise (inthe +θ_(Z) direction) when viewed from the upper side toward the lowerside.

In the following descriptions, there may be a case where thecounterclockwise forward side (−θ_(Z) side) when viewed from the upperside toward the lower side is referred to as a “rotation direction frontside” and the clockwise (−θ_(Z)) forward side (−θ_(Z) side) when viewedfrom the upper side toward the lower side is referred to as a “rotationdirection back side”.

The impeller 30 is disposed above the motor 40. The impeller 30 is fixedto the upper end portion of the shaft 41. Thus, the impeller 30 isrotatable (in the ±θ_(Z) directions) about the center axis J extendingin the up-down direction.

The impeller 30 preferably includes an impeller body portion 31, aplurality of blade portions 32 and a shroud portion 33. The impellerbody portion 31 is a portion fixed to the shaft 41. The upper surface ofthe impeller body portion 31 is a gentle slant surface which extendsdownward and radially outward from the center axis J.

The blade portions 32 are disposed on the upper surface of the impellerbody portion 31. The blade portions 32 extend upward from the uppersurface of the impeller body portion 31. While not shown in thedrawings, the blade portions are disposed at regular intervals in thecircumferential direction. The upper end portions of the blade portions32 are connected to the shroud portion 33.

The shroud portion 33 is disposed above the blade portions 32. Theshroud portion 33 is connected to the impeller body portion 31 via theblade portions 32. As illustrated in FIG. 2, the shroud portion 33 hasan annular shape centered at the center axis J. The shroud portion 33 isshaped to extend downward and radially outward. In other words, theshroud portion 33 preferably includes a curved surface or a slantsurface inclined with reference to the center axis J.

As illustrated in FIG. 3, the housing 20 accommodates the impeller 30and the motor 40. The housing 20 preferably includes an intake port 61,a flow path 50 and the exhaust port 62. The intake port 61 is a holeopened upward and arranged to bring the outside and inside of thehousing 20 into communication with each other. The intake port 61 isarranged above the impeller 30. As illustrated in FIGS. 1 and 2, whenseen in a plan view, the edge of the intake port 61 has a circular orsubstantially circular shape centered at the center axis J. Theplan-view shape of the edge of the intake port 61 is not limited to thecircular shape and is not particularly limited.

As illustrated in FIG. 3, the flow path 50 is provided within thehousing 20. The flow path 50 interconnects the intake port 61 and theexhaust port 62. The flow path 50 has, e.g., a scroll or substantiallyscroll shape. The flow path 50 preferably includes an upper flow path 51and a lower flow path 52. That is to say, the upper flow path 51 and thelower flow path 52 constitute the flow path 50 having a scroll orsubstantially scroll shape.

As used herein, the term “scroll shape” refers to a shape in which theradial dimension of the flow path grows larger as the flow path extendsin the circumferential direction. The expression “the flow path has ascroll shape” includes a case where at least one of the upper flow pathand the lower flow path has a scroll shape. That is to say, theexpression “the flow path has a scroll shape” includes a case where onlythe upper flow path has a scroll shape, a case where only the lower flowpath has a scroll shape and a case where both the upper flow path andthe lower flow path have a scroll shape.

The upper flow path 51 and the lower flow path 52 are disposed along theaxial direction. The lower flow path 52 is arranged below the upper flowpath 51. The lower flow path 52 is connected to the upper flow path 51.The upper flow path 51 and the lower flow path 52 will be describedlater.

As illustrated in FIG. 4, the exhaust port 62 is arranged radiallyoutward of the impeller 30. In the present preferred embodiment, theexhaust port 62 is opened in the direction (X-axis direction) orthogonalto the axial direction. As illustrated in FIG. 1, the exhaust port 62 isdefined by connecting an upper housing 21 and a lower housing 22 whichwill be described later. As illustrated in FIG. 5, the exhaust port 62is connected to the upper flow path 51 and the lower flow path 52.

In order to reduce a loss of the airflow discharged from the centrifugalfan 10, it is preferred that, for example, the opening area of theexhaust port 62 is equal to or larger than the opening area of theintake port 61. In a configuration in which the exhaust port 62 isconnected to only one of the upper flow path 51 and the lower flow path52, the axial dimension of the upper flow path 51 or the axial dimensionof the lower flow path 52 needs to be increased in order to secure theopening area of the exhaust port 62. This poses a problem in that thecentrifugal fan 10 becomes larger in the axial direction.

In contrast, according to the present preferred embodiment, the exhaustport 62 is connected to the upper flow path 51 and the lower flow path52. This makes it possible to provide the exhaust port 62 over the upperflow path 51 and the lower flow path 52. Thus, the opening area of theexhaust port can be increased without having to increase the axialdimension of the upper flow path 51 and the axial dimension of the lowerflow path 52. Accordingly, it is possible to restrain the centrifugalfan 10 from becoming larger in size.

In the present preferred embodiment, the axial dimension L2 of theportion of the exhaust port 62 connected to the lower flow path 52 islarger than the axial dimension L1 of the portion of the exhaust port 62connected to the upper flow path 51.

In FIG. 3, the airflow is indicated by thick arrows. As illustrated inFIG. 3, if the motor 40 rotates the impeller 30, an air is introducedinto the housing 20 through the intake port 61. The air introduced intothe housing 20 is blown toward the radial outer side of the impeller 30through the interior of the impeller 30, namely through the gap betweenthe shroud portion 33 and the impeller body portion 31. The air blownradially outward from the impeller 30 is moved through the upper flowpath 51 and the lower flow path 52 and is discharged to the outside ofthe housing 20 from the exhaust port 62.

As illustrated in FIGS. 1 and 2, the housing 20 preferably includes theupper housing 21 and the lower housing 22. That is to say, the housing20 is configured by interconnecting two separate members. Thus, whenassembling the centrifugal fan 10, it is possible for a worker to easilybring the impeller 30 into the housing 20. This makes it easy toassemble the centrifugal fan 10.

As illustrated in FIG. 3, the upper housing 21 accommodates the impeller30 at the radial inner side thereof. The upper housing 21 preferablyincludes an upper housing cover portion 23 and an upper housing wallportion 24.

The upper housing cover portion 23 is arranged above the impeller 30.That is to say, the upper housing cover portion overlaps with theimpeller 30 in the axial direction. The upper housing cover portion 23includes the intake port 61. That is to say, the upper housing 21includes the intake port 61. The intake port 61 axially extends throughthe upper housing cover portion 23.

The upper housing cover portion 23 preferably includes a cover inneredge portion 23 a extending downward from the inner edge of the intakeport 61. The cover inner edge portion 23 a has a tubular shape. Thelower end of the cover inner edge portion 23 a is arranged radiallyinward of an inner edge 33 a of the shroud portion 33. The intake port61 communicates with the interior of the impeller 30 through the insideof the cover inner edge portion 23 a.

The upper housing cover portion 23 is radially widened along the shapeof the shroud portion 33. The upper housing cover portion 23 is shapedto extend downward and radially outward. In other words, the upperhousing cover portion 23 preferably includes a curved surface or a slantsurface inclined with respect to the center axis J.

The upper housing wall portion 24 is connected to the lower end of theupper housing cover portion 23. The upper housing wall portion 24 isarranged radially outward of the impeller 30. The upper housing wallportion 24 surrounds the impeller 30 in the circumferential direction.As illustrated in FIG. 5, the upper housing wall portion 24 preferablyincludes a portion of the exhaust port 62.

An upper wall portion inner circumferential surface 24 a is the innercircumferential surface of the upper housing wall portion 24. Asillustrated in FIG. 3, the upper wall portion inner circumferentialsurface 24 a extends downward and radially outward. In other words, theupper wall portion inner circumferential surface 24 a is a curvedsurface or a slant surface inclined with respect to the center axis J.Thus, the air discharged radially outward from the impeller 30 can flowinto the lower flow path 52 along the upper wall portion innercircumferential surface 24 a.

As illustrated in FIG. 1, the upper housing wall portion 24 preferablyincludes a tongue portion 25. That is to say, the housing 20 preferablyincludes the tongue portion 25. The tongue portion 25 is a portion ofthe upper housing wall portion 24 connected to the exhaust port 62. Asillustrated in FIG. 4, the tongue portion 25 is arranged between theexhaust port 62 and the below-mentioned lower flow path start end 52 ain the circumferential direction. In the present preferred embodiment,the tongue portion 25 protrudes toward the side of the upper flow path51 (namely, toward the rotation direction back side (−θ_(Z) side) in theexample of FIG. 4). Preferably, the tongue portion 25 is smoothlycurved. An outer end portion 25 a is the radial outer end portion of thetongue portion 25. The outer end portion 25 a constitutes a portion ofthe rotation direction front side (+θ_(Z) side) edge of the exhaust port62.

As illustrated in FIG. 3, the lower housing 22 is attached to the lowerside of the upper housing 21. As illustrated in FIG. 2, the lowerhousing 22 preferably includes the motor cover portion 27, a lowerhousing bottom portion 28, a lower housing wall portion 26 and a closingportion 29. That is to say, the housing 20 preferably includes the motorcover portion 27.

As illustrated in FIG. 3, the motor cover portion 27 has a roofedtubular shape opened downward. The motor 40 is disposed radially inwardof the motor cover portion 27. The motor cover portion 27 covers themotor 40. As illustrated in FIGS. 2 and 3, the motor cover portion 27has a cylindrical shape centered at the center axis J. As illustrated inFIG. 3, the motor cover portion 27 has the output shaft hole 27 aaxially extending through a cover region of the motor cover portion 27.

The impeller 30 is arranged above the motor cover portion 27. Asillustrated in FIG. 4, when seen in a plan view, the motor cover portion27 substantially overlaps with the impeller 30 in its entirety.

As illustrated in FIG. 3, the lower housing bottom portion 28 extendsradially outward from the lower end of the motor cover portion 27. Thelower housing wall portion 26 extends upward from the radial outer endof the lower housing bottom portion 28. The axial position of the upperend of the lower housing wall portion 26 is flush with the axialposition of the upper surface of the motor cover portion 27. Asillustrated in FIG. 5, the lower housing wall portion 26 preferablyincludes a portion of the exhaust port 62.

As illustrated in FIG. 2, the closing portion 29 is arranged between themotor cover portion 27 and the lower housing wall portion 26 in theradial direction. The closing portion 29 is connected to the motor coverportion 27, the lower housing wall portion 26 and the lower housingbottom portion 28. Thus, the closing portion 29 closes a circumferentialportion of the gap between the motor cover portion 27 and the lowerhousing wall portion 26.

The upper surface of the closing portion 29 is arranged on the sameaxially-orthogonal plane as the upper surface of the motor cover portion27. The upper surface of the motor cover portion 27, the upper surfaceof the closing portion 29 and the upper end of the lower housing wallportion 26 are connected to one another with no difference in level.

As illustrated in FIG. 4, when seen in a plan view, the closing portion29 is arranged between the tongue portion 25 and the impeller 30 in theradial direction. The closing portion 29 is connected to the rotationdirection front side (−θ_(Z) side) edge of the exhaust port 62.

Next, the upper flow path 51 and the lower flow path 52 will bedescribed in detail. As illustrated in FIG. 3, the boundary between theupper flow path 51 and the lower flow path 52 is the boundary betweenthe upper housing 21 and the lower housing 22.

In the present preferred embodiment, the entirety of the upper flow path51 is arranged within the upper housing 21. That is to say, the upperhousing 21 preferably include the entirety of the upper flow path 51. Atleast a portion of the upper flow path 51 is arranged between the upperwall portion inner circumferential surface 24 a and the impeller 30 inthe radial direction. A housing inner circumferential surface 20 a isthe inner circumferential surface of the housing 20. The upper wallportion inner circumferential surface 24 a is a portion of the housinginner circumferential surface 20 a. That is to say, at least a portionof the upper flow path 51 is arranged between the housing innercircumferential surface 20 a and the impeller 30 in the radialdirection.

As illustrated in FIG. 4, the upper flow path 51 has an annular orsubstantially annular shape. The upper flow path extends along the upperwall portion inner circumferential surface 24 a. That is to say, theupper flow path 51 extends along the housing inner circumferentialsurface 20 a. As indicated by thick arrows in FIG. 4, the air introducedinto the upper flow path 51 from the impeller 30 flows through the upperflow path 51 in the same direction as the rotation direction of theimpeller 30 (in the +θ_(Z) direction). A part of the air flowing throughthe upper flow path 51 is introduced into the lower flow path 52 untilthe air reaches the exhaust port 62.

In the present preferred embodiment, the radial dimension L7 of theupper flow path 51 grows larger as the upper flow path 51 extends from areference position P1 toward the exhaust port 62 in the rotationdirection of the impeller 30 (in the −θ_(Z) direction). In other words,the upper flow path 51 has a scroll or substantially scroll shape. Thus,it is possible to suppress generation of an air vortex within the upperflow path 51 and to smoothly discharge the air from the exhaust port 62.This makes it possible to reduce a loss of airflow in the centrifugalfan 10.

The reference position P1 is positioned between the exhaust port 62 andthe below-mentioned lower flow path start end 52 a. In the presentpreferred embodiment, the reference position P1 is a point at which aline extending in the direction orthogonal to the exhaust port 62 (inthe X-axis direction) via the center axis J intersects the upper flowpath 51.

The radial dimension L7 of the upper flow path 51 becomes smallest inthe reference position P1. An inner end portion 25 b is the radial innerend portion of the tongue portion 25. Within a range from the referenceposition P1 to the inner end portion 25 b in the circumferentialdirection, the radial dimension L7 of the upper flow path 51 is equal tothe radial dimension L7 of the upper flow path 51 in the referenceposition P1. That is to say, the radial dimension L7 of the upper flowpath 51 becomes smallest over the range from the reference position P1to the inner end portion 25 b in the circumferential direction.

The axial dimension L3 of the upper flow path 51 illustrated in FIG. 3is equal to the internal axial dimension L5 of the upper housing wallportion 24. The axial dimension L3 of the upper flow path 51 growssmaller from the radial inner side toward the radial outer side. Theentirety of the upper flow path 51 is opened downward.

The upstream end of the upper flow path 51 is, for example, a positionwhere the radial dimension L7 of the upper flow path 51 illustrated inFIG. 4 becomes smallest. That is to say, the position of the upstreamend of the upper flow path 51 is the position where the upstream end ofthe upper flow path 51 is identical in the circumferential position withthe inner end portion 25 b of the tongue portion 25.

The term “upper flow path” refers to, e.g., an annular flow patharranged above the lower flow path having one closed end. That is tosay, in the present preferred embodiment, the radial outer portion ofthe axial gap between the impeller 30 and the motor cover portion 27illustrated in FIG. 3 is included in the upper flow path 51.

As illustrated in FIG. 2, the entirety of the lower flow path 52 isarranged inside the lower housing 22. A lower wall portion innercircumferential surface 26 a is the inner circumferential surface of thelower housing wall portion 26. A motor cover portion outercircumferential surface 27 b is the outer circumferential surface of themotor cover portion 27. A closing portion side surface 29 a is the sidesurface of the closing portion 29. That is to say, the lower housing 22preferably includes the entirety of the lower flow path 52. The lowerflow path 52 is a flow path surrounded by the upper surface of the lowerhousing bottom portion 28, the lower wall portion inner circumferentialsurface 26 a, the motor cover portion outer circumferential surface 27 band the closing portion side surface 29 a.

The housing inner circumferential surface 20 a is the innercircumferential surface of the housing 20. The lower wall portion innercircumferential surface 26 a is a portion of the housing innercircumferential surface 20 a. That is to say, the lower flow path 52 isarranged between the motor cover portion outer circumferential surface27 b and the housing inner circumferential surface 20 a.

As described above, the motor 40 is arranged radially inward of themotor cover portion 27. Thus, the motor 40 is arranged radially inwardof the lower flow path 52. Accordingly, when the motor 40 isaccommodated within the housing 20, it is possible to dispose the motor40 in a radially overlapping relationship with the lower flow path 52.It is therefore possible to reduce the size of the centrifugal fan 10 inthe axial direction.

As illustrated in FIG. 4, the lower flow path 52 extends along the lowerwall portion inner circumferential surface 26 a. That is to say, thelower flow path 52 extends along the housing inner circumferentialsurface 20 a. As indicated by thick arrows in FIG. 4, the air introducedfrom the upper flow path 51 into the lower flow path 52 flows throughthe lower flow path 52 in the same direction as the rotation directionof the impeller 30 (in the −θ_(Z) direction).

As illustrated in FIGS. 2 and 4, a lower flow path terminal end 52 b isone circumferential end (−θ_(Z) side end) of the lower flow path 52 andis opened in the exhaust port 62. A lower flow path start end 52 a isthe other circumferential end (−θ_(Z) side end) of the lower flow path52 and is closed with respect to the exhaust port 62.

Thus, within the lower flow path 52, the air guided from the lower flowpath start end 52 a toward the lower flow path terminal end 52 b doesnot flow from the vicinity of the exhaust port 62 toward the upstreamside, namely the side of the lower flow path start end 52 a.Accordingly, the entirety of the air flowing through the lower flow path52 is discharged from the exhaust port 62. This makes it possible toreduce a loss of airflow.

If the air flowing toward the vicinity of the exhaust port 62 impingesagainst the tongue portion 25 (see FIG. 4), a turbulent flow of air isgenerated in the vicinity of the tongue portion 25. This poses a problemin that a noise is generated by the turbulent flow.

In contrast, according to the present preferred embodiment, the lowerflow path start end 52 a is closed with respect to the exhaust port 62.For that reason, a tongue portion is not provided within the lower flowpath 52. Thus, the air flowing through the lower flow path 52 does notimpinge against a tongue portion. This makes it possible to suppressgeneration of a turbulent flow of air. As a result, it is possible tosuppress generation of a noise.

Referring to FIG. 4, a straight line passing through the center axis Jand the center P2 of the exhaust port 62 is referred to as a “straightline C3”. As used herein, the term “the vicinity of the exhaust port”includes a range in which the circumferential angle θ2 from the straightline C3 toward the rotation direction back side (−θ_(Z) side) becomes 75degrees or less. The center P2 of the exhaust port 62 is, for example,the center of the exhaust port 62 in the direction orthogonal to thecenter axis J and parallel to the exhaust port 62 (in the Y-axisdirection).

As illustrated in FIG. 5, all the upper flow path 51 and the lower flowpath 52 are connected to the exhaust port 62. The upper flow path 51 hasan annular or substantially annular shape. Thus, there is a possibilitythat a part of the air guided from the interior of the upper flow path51 toward the vicinity of the exhaust port 62 flows toward the upstreamside of the upper flow path 51. Furthermore, there is a possibility thatthe air flowing toward the upstream side of the upper flow path 51impinges against the tongue portion 25 and generates a noise.

In contrast, according to the present preferred embodiment, the axialdimension L2 of the portion of the exhaust port 62 connected to thelower flow path 52 is larger than the axial dimension L1 of the portionof the exhaust port 62 connected to the upper flow path 51. This makesit possible to reduce the flow rate of the air flowing through the upperflow path 51. It is therefore possible to restrain the air guided to thevicinity of the exhaust port 62 from flowing toward the upstream side ofthe upper flow path 51. Accordingly, it is possible to further reduce aloss of airflow and to further suppress generation of a noise.

In the case of closing one circumferential end of the lower flow path,it is preferable that one end of the lower flow path is closed in thecircumferential direction. That is to say, even when closing onecircumferential end of the lower flow path, one circumferential end ofthe lower flow path may be opened upward.

As illustrated in FIGS. 2 and 4, the lower flow path start end 52 a isclosed by the closing portion 29. That is to say, the circumferentialposition of the lower flow path start end 52 a is the same as thecircumferential position of the rotation direction front side (+θ_(Z)side) end of the closing portion 29.

Preferably, the lower flow path start end 52 a is arranged near theexhaust port 62 in the circumferential direction. If the lower flow pathstart end 52 a is excessively spaced apart from the exhaust port 62 inthe circumferential direction, the length of the lower flow path 52becomes small. For that reason, the air discharged from the impeller 30is not efficiently guided to the exhaust port 62. Thus, the blowingefficiency of the centrifugal fan 10 is reduced.

Referring to FIG. 4, when seen in a plan view, a straight line C2 is astraight line passing through the center axis J and meeting with thelower flow path start end 52 a. A straight line C1 is a straight linepassing through the center axis J and meeting with the tongue portion25. The angle between the straight line C1 and the straight line C2 isassumed to be θ. The circumferential angle from the straight line C1 isassumed to be θ1. In this case, it is preferred that the angle θ is 75degrees or less. That is to say, when seen in a plan view, the lowerflow path start end 52 a is located in the position where thecircumferential angle θ1 from the straight line C1 becomes 75 degrees orless. The angle θ1 is a circumferential angle from the straight line C1toward the rotation direction front side (+θ_(Z) side).

By positioning the lower flow path start end 52 a within this angularextent, it is possible to have the circumferential position of the lowerflow path start end 52 a lie near the exhaust port 62. It is thereforepossible to suppress reduction of the blowing efficiency of thecentrifugal fan 10.

The radial dimension L8 of the lower flow path 52 grows larger from thelower flow path start end 52 a toward the lower flow path terminal end52 b. That is to say, the lower flow path 52 has a scroll or asubstantially scroll shape. It is therefore possible to suppressgeneration of an air vortex within the lower flow path 52 and tosmoothly discharge the air from the exhaust port 62. This makes itpossible to further reduce a loss of airflow.

Furthermore, the upper housing wall portion 24 constitutes the radialouter inner circumferential surface of the upper flow path 51. The lowerhousing wall portion 26 constitutes the radial outer innercircumferential surface of the lower flow path 52. In the presentpreferred embodiment, the upper flow path 51 has a scroll shape or asubstantially scroll shape. This makes it easy to interconnect the upperhousing 21 having the upper flow path 51 and the lower housing 22 havingthe lower flow path 52. Specifically, the upper housing wall portion 24and the lower housing wall portion 26 may be shaped to go away from thecenter axis J as they extend in the circumferential direction. Thismakes it easy to connect the upper housing wall portion 24 to the lowerhousing wall portion 26.

In the present preferred embodiment, the axial dimension L4 of the lowerflow path 52 illustrated in FIG. 3 is uniform. The axial dimension L4 ofthe lower flow path 52 is equal to the internal axial dimension L6 ofthe lower housing 22. This makes it easy to increase the axial dimensionL4 of the lower flow path 52.

The flow velocity of the air flowing through the flow path 50 tends tobecome larger in the position closer to the lower housing bottom portion28. If the air having a large flow velocity is introduced from thevicinity of the exhaust port 62 toward the upstream side of the flowpath 50, the loss of airflow grow larger. Moreover, the air having alarge flow velocity impinges against the tongue portion 25. Thus, aturbulent flow is easily generated and a noise is increased. Theupstream side of the flow path 50 is, for example, the upstream side ofthe upper flow path 51.

In contrast, according to the present preferred embodiment, it ispossible to increase the axial dimension L4 of the lower flow path 52.This makes it possible to reliably prevent the air having a large flowvelocity from being introduced toward the upstream side of the flow path50. Accordingly, it is possible to further reduce the loss of airflow.

As illustrated in FIGS. 2 and 4, the entirety of the lower flow path 52is opened upward toward the upper flow path 51. For that reason, the airdischarged radially outward from the impeller 30 is easily introducedfrom the upper flow path 51 into the lower flow path 52. This makes iteasy to discharge the air from the exhaust port 62 via the lower flowpath 52. Accordingly, it is possible to further reduce the loss ofairflow.

As illustrated in FIG. 3, the axial dimension L4 of the lower flow path52 is larger than the axial dimension L3 of the upper flow path 51. Forthat reason, the air discharged radially outward from the impeller 30easily flows from the upper flow path 51 toward the lower flow path 52.This makes it possible to further reduce the loss of airflow.

The present disclosure is not limited to the configurations describedabove. In the following descriptions, there may be a case where the sameconfigurations as described above are appropriately designated by likereference symbols with the descriptions thereof omitted.

One of the upper flow path 51 and the lower flow path 52 may not have ascroll shape. In this case, one of the upper flow path 51 and the lowerflow path 52 may have, e.g., an annular or substantially annular shape.A portion of the lower flow path 52 may not be opened toward, e.g., theupper flow path 51.

The lower housing 22 may have a portion of the upper flow path 51 andthe lower flow path 52. In this case, the axial dimension L4 of thelower flow path 52 in the vicinity of the exhaust port 62 may be onehalf or more of the internal axial dimension L6 of the lower housing 22.According to this configuration, it is possible to sufficiently increasethe axial dimension L4 of the lower flow path 52 and to prevent the airhaving a large flow velocity from flowing from the vicinity of theexhaust port 62 toward the upstream side of the upper flow path 51.

In the configuration in which the lower housing 22 has a portion of theupper flow path 51 and the lower flow path 52, for example, the axialposition of the upper surface of the closing portion 29 illustrated inFIG. 2 may be lower than the axial position of the upper surface of themotor cover portion 27. In this case, the internal portion of the lowerhousing 22 arranged higher than the closing portion 29 has an annular orsubstantially annular shape. Thus, within the lower housing 22, aportion of the upper flow path 51 is provided above the upper surface ofthe closing portion 29, and the lower flow path 52 is provided below theupper surface of the closing portion 29.

FIG. 6 is a side view illustrating a centrifugal fan 110 according toanother example of one preferred embodiment. As illustrated in FIG. 6,the exhaust port 62 may be connected to only the lower flow path 52.

As illustrated in FIG. 6, the centrifugal fan 110 preferably includes ahousing 120. The housing 120 preferably includes an intake port 61, aflow path 50 and an exhaust port 162. The housing 120 preferablyincludes an upper housing 121 and a lower housing 122.

The upper housing 121 preferably includes an upper housing cover portion23 and an upper housing wall portion 124. The configuration of the upperhousing wall portion 124 is the same as the configuration of the upperhousing wall portion 24 illustrated in FIG. 5, except that the upperhousing wall portion 124 does not have a portion of the exhaust port 62.In FIG. 6, the upper housing wall portion 124 has a shape obtained byclosing a portion of the exhaust port 62 defined by the upper housingwall portion 24 illustrated in FIG. 5.

The lower housing 122 preferably includes a lower housing bottom portion28, a lower housing wall portion 126 and a closing portion 29. While notshown in the drawings, the lower housing 122 includes a motor coverportion 27. The configuration of the lower housing wall portion 126 isthe same as the configuration of the lower housing wall portion 26illustrated in FIG. 5, except that the lower housing wall portion 126has the entirety of the exhaust port 162.

In this configuration, the exhaust port 162 is connected to only thelower flow path 52. For that reason, the entirety of the air dischargedfrom the exhaust port 162 is discharged from the lower flow path 52. Itis therefore possible to enable the air existing within the upper flowpath 51 to easily flow toward the lower flow path 52 while the air flowsfrom the upstream side of the upper flow path 51 to the vicinity of theexhaust port 162. Accordingly, it is possible to further restrain theair from flowing from the vicinity of the exhaust port 162 toward theupstream side of the upper flow path 51. As a result, it is possible tofurther reduce the loss of airflow and to further suppress generation ofa noise.

In this configuration, the axial dimension of the lower housing 122 maybe made larger than the axial dimension of the lower housing 22 (seeFIG. 5). By doing so, it is possible to set the opening area of theexhaust port 162 larger than the opening area of the intake port 61.

Other configurations of the exhaust port 162 are the same as theconfigurations of the exhaust port 62 illustrated in FIG. 5. Otherconfigurations of the centrifugal fan 110 are the same as theconfigurations of the centrifugal fan 10 illustrated in FIG. 5.

FIG. 7 is a sectional view illustrating a portion of a centrifugal fan210 according to a further example of one preferred embodiment. Asillustrated in FIG. 7, the lower end portion of the lower flow path 52may be a slant surface.

As illustrated in FIG. 7, the centrifugal fan 210 preferably includes ahousing 220. The housing 220 preferably includes a flow path 250. Theflow path 250 preferably includes an upper flow path 51 and a lower flowpath 252. The housing 220 preferably includes an upper housing 21 and alower housing 222. The lower housing 222 preferably includes a lowerhousing bottom portion 228, a lower housing wall portion 26 and aclosing portion 29. While not shown in the drawings, the lower housing222 preferably includes a motor cover portion 27.

A bottom surface 228 a of the lower housing bottom portion 228 is aslant surface. The bottom surface 228 a extends downward in the portionconnected to the closing portion 29. That is to say, the bottom surface228 a extends downward from a lower flow path start end 252 a toward therotation direction front side (+θ_(Z) side). In other words, the bottomsurface 228 a is a slant surface inclined with respect to the centeraxis J or a curved surface. In the portion connected to the closingportion 29, the axial position of the bottom surface 228 a is preferablythe same as the axial position of the upper surface of the closingportion 29. That is to say, at the lower flow path start end 252 a, theaxial position of the bottom surface 228 a is preferably the same as theaxial position of the upper surface of the closing portion 29.

The bottom surface 228 a is the lower end portion of the lower flow path252. The position of the lower end portion of the lower flow path 252goes away from the upper flow path 51 as the lower flow path 252 extendsfrom the lower flow path start end 252 a toward the lower flow pathterminal end (not illustrated). In other words, the distance between thelower end portion of the lower flow path 252 and the upper flow path 51grows larger from the lower flow path start end 252 a toward the lowerflow path terminal end (not illustrated). Thus, the axial dimension ofthe lower flow path 252 becomes larger from the lower flow path startend 252 a toward the lower flow path terminal end.

The air introduced from the intake port 61 into the impeller 30 isdischarged from the circumferential entirety of the impeller 30 to theupper flow path 51. A part of the air introduced into the upper flowpath 51 flows toward the lower flow path 52 while moving through theupper flow path 51 in the rotation direction of the impeller 30 (−θ_(Z)direction). For that reason, at the upstream side of the upper flow path51 from which the air begins to flow, the amount of the air flowing fromthe upper flow path 51 toward the lower flow path 52 is small. Thus, forexample, in the case where the axial dimension of the lower flow path 52is uniform over the entirety of the lower flow path 52, the air tends tostay within the lower flow path 52 in the vicinity of the lower flowpath start end 52 a. Thus, an air vortex is easily generated.Accordingly, there is a possibility that the loss of airflow becomeslarger.

In contrast, according to the aforementioned configuration, the lowerend portion of the lower flow path 252 goes away from the upper flowpath 51 as the lower flow path 252 extends from the lower flow pathstart end 252 a toward the lower flow path terminal end. In other words,the distance between the lower end portion of the lower flow path 252and the upper flow path 51 grows larger from the lower flow path startend 252 a toward the lower flow path terminal end. Thus, it is possibleto reduce the axial dimension of the lower flow path 252 at the upstreamside where the amount of the air introduced from the upper flow path 51into the lower flow path 252 is small. This makes it possible torestrain the air from staying within the lower flow path 252.Accordingly, it is possible to restrain the loss of airflow frombecoming larger.

At the downstream side, the amount of the air introduced from the upperflow path 51 into the lower flow path 252 is large. According to thisconfiguration, it is possible to increase the axial dimension of thelower flow path 252 at the downstream side. Thus, it is possible toenable the air to efficiently flow from the upper flow path 51 towardthe lower flow path 252.

According to the configuration described above, as indicated by thickarrows in FIG. 7, it is possible to enable the air to smoothly flowalong the bottom surface 228 a which is a slant surface. This makes itpossible to enable the air to smoothly flow through the flow path 250,thereby further suppressing generation of an air vortex within the flowpath 250.

Preferably, the axial dimension of the lower flow path 252 in thevicinity of the exhaust port 62 is, for example, one half or more of theaxial dimension of the lower housing 222. This makes it possible tofurther reduce the loss of airflow.

According to the configuration described above, it is possible tofurther improve the blowing efficiency of the centrifugal fan 210. Otherconfigurations of the centrifugal fan 210 are the same as theconfigurations of the centrifugal fan 10 illustrated in FIGS. 1 to 5.

Furthermore, the upper housing 21 may have the entirety of the upperflow path 51 and the entirety of the lower flow path 52. The housing 20may be configured by axially interconnecting three or more independentmembers. The housing 20 may be a single member.

The upper housing 21 may not include the tongue portion 25. The motor 40may not be accommodated within the housing 20.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A centrifugal fan comprising: an impellerarranged to rotate about a center axis extending in an up-downdirection; a motor arranged below the impeller and arranged to rotatethe impeller about the center axis; and a housing arranged toaccommodate the impeller, wherein the housing includes an intake portarranged above the impeller, an exhaust port arranged radially outwardof the impeller, an annular upper flow path at least partially arrangedbetween a housing inner circumferential surface as an innercircumferential surface of the housing and the impeller in a radialdirection, and a lower flow path arranged below the upper flow path andconnected to the upper flow path, the upper flow path and the lower flowpath are arranged to define a flow path having a scroll shape, the lowerflow path extends along the housing inner circumferential surface, thelower flow path has a lower flow path terminal end as onecircumferential end thereof opened toward the exhaust port, and thelower flow path has a lower flow path start end as the othercircumferential end thereof closed with respect to the exhaust port. 2.The fan according to claim 1, wherein a radial dimension of the lowerflow path grows larger from the lower flow path start end toward thelower flow path terminal end.
 3. The fan according to claim 1, whereinthe housing includes an upper housing having the intake port and a lowerhousing attached to a lower side of the upper housing.
 4. The fanaccording to claim 3, wherein the lower housing includes a portion ofthe upper flow path and the lower flow path, and an axial dimension ofthe lower flow path in the vicinity of the exhaust port is one half ormore of an internal axial dimension of the lower housing.
 5. The fanaccording to claim 3, wherein the upper housing includes an upperhousing cover portion having the intake port and overlapping with theimpeller in an axial direction and a upper housing wall portionconnected to a lower end of the upper housing cover portion and arrangedto surround the impeller in a circumferential direction, and the upperhousing wall portion has an inner circumferential surface extendingdownward and radially outward.
 6. The fan according to claim 1, whereina radial dimension of the upper flow path grows larger as the upper flowpath extends from a reference position existing between the exhaust portand the lower flow path start end toward the exhaust port in a rotationdirection of the impeller.
 7. The fan according to claim 1, wherein theexhaust port is connected to the upper flow path and the lower flowpath.
 8. The fan according to claim 7, wherein an axial dimension of aportion of the exhaust port connected to the lower flow path is largerthan an axial dimension of a portion of the exhaust port connected tothe upper flow path.
 9. The fan according to claim 1, wherein theexhaust port is connected to only the lower flow path.
 10. The fan ofclaim 1, wherein a position of a lower end portion of the lower flowpath goes away from the upper flow path as the lower flow path extendsfrom the lower flow path start end toward the lower flow path terminalend.
 11. The fan according to claim 1, wherein an axial dimension of thelower flow path is larger than an axial dimension of the upper flowpath.
 12. The fan according to claim 1, wherein the entirety of thelower flow path is opened toward the upper flow path.
 13. The fanaccording to claim 1, wherein the housing includes a tongue portionarranged between the exhaust port and the lower flow path start end in acircumferential direction, and when seen in a plan view, the lower flowpath start end is located in a position where a circumferential anglefrom a straight line passing through the center axis and meeting withthe tongue portion becomes 75 degrees or less.
 14. The fan according toclaim 1, wherein the motor is arranged radially inward of the lower flowpath, the housing includes a motor cover portion arranged to cover themotor, and the lower flow path is arranged between an outercircumferential surface of the motor cover portion and the housing innercircumferential surface.